U.S. Pat. No. 7,411,012 discloses the use of alkyl pyrrolidones as plasticizers to provide long term plastification to PVC so as to impart flexibility, softness, extensibility and or/lower melting temperature to PVC compositions. International Publication No. WO2009/126552 discloses a stabilized, plasticized PVC composition including an alkyl pyrrolidone plasticizer and an organic phosphite ester stabilizer. The disclosed compositions exhibit excellent early color performance and heat stability at higher temperatures. The present application further demonstrates improvements in the processing conditions of PVC compositions used in the production of flexible, semi-rigid, rigid PVC.
Poly(vinyl chloride), hereafter referred to as PVC, is extensively used in many applications. In use, additives such as plasticizers, thermal stabilizers, lubricants, pigments, fillers, impact modifiers, and flame retardants are generally employed to produce PVC compositions having desired properties.
One of the major hurdles during processing of PVC is the requirement of high temperature that tends to degrade PVC ultimately by various processes like dehydrochlorination, auto-oxidation, mechano-chemical chain scission, cross linking of macromolecules and condensation reactions. These changes lead to altered physio-mechanical and rheological properties of PVC.
Rigid and semi rigid applications of PVC have enormous commercial value. Around 70% of the total PVC volume is used for manufacturing of rigid PVC goods (like pipes and tubes, window and door profiles, rigid sheets, packaging and many others). Since the processing temperature of rigid and semi-rigid PVC is significantly higher than flexible PVC, which typically contains a large amount of plasticizers, there is need for additives for lowering the gelling temperatures, increasing the gelling speed and homogeneity.
Plasticizers can produce so called anti-plasticizing effect when used at lower levels from about 3 phr to about 15 phr. In semi-rigid applications commonly 20 to 30 phr of the plasticizers are used. Below those levels a plasticizing effect is typically not noticeable.
As disclosed in WO 2007/059123, alkyl pyrrolidone with different alkyl moieties can effectively plasticize PVC, in an amount from 5 to 100 phr, for sufficiently long term. By lowering the processing temperatures, alkyl pyrrolidones can also facilitate heat stabilization of the composition.
However, processing of PVC involves a number of other challenges such as keeping the gelling temperature low so as to reduce the manufacturing or processing cost and controlling the gelling speed. High haze that can result from other additives is also highly undesirable.
Thus it would be beneficial to have a cost effective additive blend that can reduce the processing complexities and simplify the manufacturing process.
Accordingly, in accordance with one aspect, a PVC composition comprising an additive that improves processing is disclosed. The additive comprises a blend of alkyl pyrrolidones in an amount of 0.1 to 20 phr sufficient to improve PVC processing.
More particularly, the additive can result in an improvement in the manufacturing process of rigid/semi-rigid/flexible PVC goods. Examples of the types of improvements that may be realized include decreased gelling temperature; increased gelling speed; transparency and homogeneity; reduced haze and hardness; improved melt flow; impact resistance and filler compatibility; increased cold flexibility; and improved crack resistance.